The internet offers possibilities to form communities and share a sense of humour that might not be acceptable in other spheres of public discourse. The internet also provides possibilities to develop and subvert text genres, such as dictionaries. There are serious slang dictionaries, but UrbanDictionary.com lies where humour and subversion meet. This article explores how the genre conventions of dictionaries are used and expanded to create a subversion of lexicographical standards and how these instances of subversion may result in humorous content. Also, the semantic properties of the entries, namely those based on metaphors, will be analysed with respect to how far these play a role in creating the specific genital humour UrbanDictionary.com is known for. For this, theories of metaphoric humour will be expanded to see how unexpected mapping processes result in incongruity and configurational humour.